In accordance with provisions of present industry standards of an optical module (such as SFP, SFP+, QSFP+, CFP, CFP2 and CFP4) for signals of an optical fiber connector, an optical interface and an electrical interface of a transmitter or a receiver are designed to be arranged on a modular structure from left to right in X direction, while a transmitting interface and a receiving interface of the optical fiber connector are designed to be arranged in the same horizontal plane parallel to the X axis from left to right (please refer to FIG. 1, a schematic diagram illustrating an optical fiber connector in a QSFP+ module in the prior art where the transmitting interface and the receiving interface are arranged from left to right, and in which T represents the transmitting interface, and R represents the receiving interface), and a transmitter high-speed signal interface and a receiver high-speed signal interface of electrical interfaces of a printed circuit board are also designed to be arranged on the printed circuit board from left to right.
In the prior art, a transmitter optical component and a receiver optical component are arranged inside the optical module from left to right accordingly, that is, the transmitter optical component and the receiver optical component correspond to the transmitting interface and the receiving interface of the optical fiber connector. Also take an example of the structure of the QSFP+ module in the prior art. Please refer to FIG. 2, which is a schematic diagram illustrating a QSFP+ module in the prior art where the transmitter optical component and the receiver optical component are arranged from left to right. As shown, the QSFP+ module includes a housing 1, an optical fiber connector 2, a transmitter optical component 3, a receiver optical component 4 and a printed circuit board 5 within the housing 1. The transmitter optical component 3 and the receiver optical component 4 are coupled to the optical fiber connector 2, and are electrically connected to the printed circuit board 5. The transmitter optical component 3 and the receiver optical component 4 are arranged in the housing 1 from left to right. In such arrangement, the transmitter optical component and the receiver optical component are limited and can only use a half of the module's width respectively, resulting in following defects of the optical module.
Firstly, the transmitter optical component and the receiver optical component can only use a half of the module's width respectively, so the layout of high-speed devices and high-speed signals related to the transmitter optical component, the receiver optical component, the printed circuit board and the electrical connection devices therebetween is restrained. In other words, the layout of the transmitter optical component and the receiver optical component arranged side by side in the prior art brings some limitations to the design of the electric circuit and the optical path in the optical module. In addition, the space limitation may result in a limited gap between signal channels in the optical modules, so that it is easy to cause crosstalk between the signal channels.
Secondly, the transmitter optical component generates more heat than the receiver optical component, so the layout of the transmitter optical component and the receiver optical component arranged side by side will cause heat mainly concentrated on one side of the optical module, which is bad for heat dissipation of the transmitter optical component, and further influencing the heat dissipation effect of the whole optical module.
In addition, in the prior art, a typical printed circuit board includes a substrate, a transmitter optical component interface, a receiver optical component interface and an electrical interface, with the electrical interface further including a transmitter data interface and a receiver data interface. The transmitter optical component interface and the receiver optical component interface of the printed circuit board are arranged on a surface of the substrate, the transmitter optical component interface is configured to be coupled to a transmitter optical component in the optical module, and the receiver optical component interface is configured to be coupled to a receiver optical component in the optical module. In the prior art, the transmitter optical component and the receiver optical component in the optical module are arranged on the modular structure from left to right in X direction, so the transmitter optical component interface and the receiver optical component interface are arrange on the surface of the substrate side by side accordingly. The transmitter data interface and the receiver data interface of the printed circuit board are also arranged on the surface of the substrate, and the transmitter data interface and the receiver data interface are designed to be arranged on the substrate to the left and to the right respectively, according to the present optical module industry standards (such as SFP, SFP+, QSFP+, CFP, CFP2 and CFP4). Please refer to FIG. 3, which is a schematic diagram showing the definition of the electrical interface of the printed circuit board in a QSFP+ module in the prior art. As shown, the electrical interface is designed to have 38 contacts, wherein the transmitter data interface in the electrical interface is arranged on the upper and lower surfaces of the substrate (hereinafter referred to as first surface and second surface respectively), the receiver data interface in the electrical interface is arranged on the upper and lower surfaces of the substrate, and the transmitter data interface and the receiver data interface are arranged on the substrate side by side. In other words, some of the contacts of the transmitter data interface are arranged on the first surface and the other contacts of the transmitter data interface are arranged on the second surface, and the contacts on the first surface and the contacts on the second surface are both arranged on the left (or right) of the substrate; and some of the contacts of the receiver data interface are arranged on the first surface and the other contacts of the receiver data interface are arranged on the second surface, and the contacts on the first surface and the contacts on the second surface are both arranged on the right (or left) of the substrate. In the printed circuit board, the transmitter optical component interface and the transmitter data interface are coupled with each other by wiring on the printed circuit board to form a transmitter data transmission path, and the receiver optical component interface and the receiver data interface are coupled with each other by wiring on the printed circuit to form a receiver data transmission path.
The above printed circuit board in the prior art has the following disadvantages. Firstly, the transmitter data transmission path and the receiver data transmission path are arranged on the same surface of the printed circuit board, so it causes crosstalk between the transmitter data transmission path and the receiver data transmission path. Secondly, the transmitter optical component interface and the receiver optical component interface are arranged on one surface of the printed circuit board, while the transmitter data interface and the receiver data interface are arranged on two surfaces of the printed circuit board, so when the transmitter data transmission path and the receiver data transmission path are formed, some circuit board wires on one surface of the printed circuit board are required to be connected to the other surface of the printed circuit board via one or more via holes, which causes the signal integrity worse.